The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
The human anatomy includes many types of tissue that can either voluntarily or involuntarily, perform certain functions. However, after disease or injury, certain tissues may no longer operate within general anatomical norms. For example, after disease, injury, age, or combinations thereof, the heart muscle may begin to experience certain failures or deficiencies. Some of these failures or deficiencies can be corrected or treated with implantable medical devices (IMDs). These devices can include implantable pulse generator (IPG) devices, pacemakers, implantable cardioverter-defibrillator (ICD) devices, cardiac resynchronization therapy defibrillator devices, implantable monitoring or diagnostic devices, neurostimulators or combinations thereof.
The IMD may include a lead that is directly connected to tissue to be affected by the IMD. The lead can include a tip portion that is directly connected to the anatomical tissue, such as a muscle bundle, and a lead body that connects to the device body or therapeutic driving device. It is generally known that the device body or case portion can be implanted in a selected portion of the anatomical structure, such as in a chest or abdominal wall, and the lead can be inserted through various venous portions so that the tip portion can be positioned at the selected position near or in the muscle group.
The IMD generally remains with the patient during the rest of the patient's natural life. To that end, the IMD can be exposed to various environmental factors. For example, the patient may undergo a magnetic resonance imaging (MRI) procedure or other high frequency imaging procedures. Magnetic resonance imaging has been developed as an imaging technique adapted to obtain both images of anatomical features of human patients as well as some aspects of the functional activities of biological tissue. These images have medical diagnostic value in determining the state of the health of the anatomical tissue examined.
In a magnetic-resonance imaging process, a patient is typically aligned to place the portion of the patient's anatomy to be examined in the imaging volume of the magnetic-resonance imaging apparatus. Such a magnetic-resonance imaging apparatus typically comprises a primary magnet for supplying a constant magnetic field which, by convention, is along the z-axis and is substantially homogeneous over the imaging volume and secondary magnets that can provide linear magnetic field gradients along each of three principal Cartesian axes in space. A magnetic field gradient refers to the variation of the field with respect to each of the three principal Cartesian axes.
The use of the magnetic-resonance imaging process with patients who have implanted medical devices, such as cardiac assist devices, often presents problems. As is known to those skilled in the art, implantable devices (such as implantable pulse generators and cardioverter/defibrillator/pacemakers) are sensitive to a variety of forms of electromagnetic interference because these enumerated devices include sensing and logic systems that respond to low-level electrical signals emanating from the monitored tissue region of the patient. Since the sensing systems and conductive elements of these implantable devices are responsive to changes in local electromagnetic fields, the implanted devices are vulnerable to external sources of severe electromagnetic noise, and in particular, to electromagnetic fields emitted during the magnetic resonance imaging procedure. Thus, patients with implantable devices are generally advised not to undergo magnetic resonance imaging procedures since one or more leads of the IMD may act as an antenna and have current or energy induced therein due to the MRI procedure. This induced current or energy can damage the IMD or anatomical tissue and cause injury to the patient. Accordingly, reduction or dissipation of the induced current or energy would be useful and beneficial to patients having an implanted medical device.